The present invention relates to a projection lens shifting mechanism of a projector apparatus for projecting a light beam from a light source such as a lamp onto a screen by way of a projection lens to make an enlarged projection of an image rendered on a display device such as a liquid crystal panel
Conventionally, a liquid crystal projector apparatus, in which a liquid crystal display panel is provided, has been employed to make an enlarged projection of an image in a personal computer display or video device. The liquid crystal projector generates a light signal of a picture by transmitting or screening the light projected from the lamp light source, in response to the image of the liquid crystal display panel.
The liquid crystal display panel is made up of liquid crystal elements arranged in a two-dimensional plane on a liquid crystal panel, and a projection lens serves the enlarged projection of the image to present a picture on a screen. The projection lens is normally equipped with a cam and screw mechanism whereby the lens-barrel can be rotated to shift a part of a plurality of lenses in the direction of the optical axis to adjust focus and zoom.
The position of the projection lens in a liquid crystal projector is typically fixed with respect to the liquid crystal panel, and the position and size of the picture projected onto the screen is therefore determined by the relative positions of the screen and projector. In order to project a picture of the proper size onto the proper position of the screen, the projector must be adjusted to the proper relative position with respect to the screen, and considerable time and effort are therefore required to position the projector.
In many liquid crystal projectors, the projection lens is shifted in advance to a fixed height above the liquid crystal panel and then secured. Thus, by projecting the light beam from the fixed height shifted upward with respect to the liquid crystal panel, a picture can be projected onto a screen at a high position to facilitate viewing regardless of the height of the stand on which the projector is set up. When it is desired to shift the position of the picture on the screen still higher, the projection direction is shifted upward by means of a height adjustment mechanism attached to the forward legs of the projector. In such a case, however, since the angle between the liquid crystal panel surface and the screen surface changes, the picture that should be projected, for example, as a square is distorted to a trapezoid. To eliminate this distortion, the inclination of the screen must be adjusted according to the inclination of the liquid crystal panel, and it was therefore necessary to provide a screen having a tilting mechanism.
To solve this problem, some high-function liquid crystal projectors are provided with a mechanism for electric-powered shifting of the projection lens by means of, for example, a motor. However, such devices necessitate a complex mechanism to enable vertical and horizontal movement while accurately holding the heavy projection lens. This requirement results in an increase in cost. The following examples have been proposed in the prior art as liquid crystal projectors provided with mechanisms for moving the projection lens.
A liquid crystal projector is disclosed in Japanese Utility Model Laid-open No. 21246/1993 (hereinbelow referred to as the first example of the prior art) in which a projection lens is supported by a pantograph mechanism constituted by four control links and in which rotating of a dial drives the pantograph mechanism to enable vertical movement of the projection lens.
A method of adjusting the alignment of a liquid crystal panel in a liquid crystal projector is disclosed in Japanese Patent Laid-open No. 107434/1993 (hereinbelow referred to as the second example of the prior art). According to this method, a liquid crystal panel holding part is constituted by a bracket secured to a base plate and a liquid crystal attachment plate secured to this bracket by means of securing screws. A jig is used for shifting the liquid crystal attachment plate with respect to the bracket, and after adjusting the position of the liquid crystal attachment plate by means of adjustment screws of the jig, the bracket and liquid crystal attachment plate are secured by the securing screws. The jig is then removed.
A projection display device in which the projection lens can be moved vertically by means of a projection-lens moving mechanism is disclosed in Japanese Patent Laid-open No. 196888/1993 (hereinbelow referred to as the third example of the prior art). This projection-lens moving mechanism is provided with a lead screw that is rotatably borne by a housing and a projection-lens holding member having a threaded hole that engages with this lead screw such that the projection-lens holding member moves up and down with rotation of this lead screw. This lead screw is provided with a knob for rotating the screw. The projection lens holding member, being accommodated inside the housing, can both hold the projection lens and translate while being guided vertically by the rotation of the lead screw. The projection lens holding member is thus movable vertically by rotating the knob.
A liquid crystal projector is disclosed in Japanese Patent Laid-open No. 249409/1993 (hereinbelow referred to as the fourth example of the prior art) in which a projection lens is installed in a projector body so as to allow horizontal and vertical movement of the projection lens by magnetic force or by leaf springs and in which the user applies force manually against the projection lens to move the projection lens.
A liquid crystal projector is disclosed in Japanese Patent Laid-open No. 138377/1997 (hereinbelow referred to as the fifth example of the prior art) in which light from a light source is collimated by a first condenser lens to a substantially parallel light beam and incident on a liquid crystal panel, this light beam is optically modulated in response to a video signal that is externally supplied to the liquid crystal panel, and the modulated light beam emitted from the liquid crystal panel is then condensed by a second condenser lens to enter a projection lens to present a picture on a screen. In this liquid crystal projector, when the position of projection on the screen is to be moved up and down, a motor provided for shifting the projection lens is activated and a link mechanism that supports the projection lens is moved in a vertical direction.
A liquid crystal projector is disclosed in Japanese Patent Laid-open No. 258565/1999 (hereinbelow referred to as the sixth example of the prior art) in which pictures from two projectors are superimposed on each other on a screen in order to brighten the picture projected on the screen. In the lens moving mechanism for shifting the position of projection on the screen, a lead screw rod is rotatably attached to the housing of the liquid crystal projector and a nut to be engaged with the lead screw is secured to the lens-barrel of the projection lens. When the lead screw rod is rotated by operating a control member provided on the side surface of the housing, the nut moves to cause the lens-barrel to move in a vertical direction. This lens moving mechanism is basically equivalent to the previously described third example of the prior art, but differs from the third example of the prior art in that the lead screw rod tilts forward. The reason for this is to compensate for change in the size of the projected picture that is brought about by a change in the distance between the liquid crystal panel and projection lens caused by the vertical movement of the projection lens.
Thus, although a number of liquid crystal projectors provided with projection lens moving mechanisms have been proposed in the prior art, the projection lens moving mechanism disclosed in the first example of the prior art has the problem of large-scale structure resulting from the use of a pantograph mechanism. The second example of the prior art is a method of adjusting the alignment of a liquid crystal panel and therefore has an object differing from that of the present invention, which is directed to adjusting the position of the projection lens. The second example of the prior art is further directed to using a jig to make a single initial adjustment of the liquid crystal panel and is not directed to a construction for making adjustments with each use of the liquid crystal projector as in the present invention.
The projection lens moving mechanism disclosed in the third example of the prior art has the problem of bulky and heavy construction.
The reason for this is that it is provided with a lead screw that is rotatably borne by the housing; a knob for rotating this lead screw; and a projection-lens holding member for supporting the projection lens having a threaded hole to be engaged with the lead screw to enable vertical movement with rotation of the lead screw.
In the projection lens moving mechanism of the fourth example of the prior art, the projection lens is semi-secured to the projector body by magnetic force or by a leaf spring. Since the projection lens is in a semi-secured state both during and after a user applies manual force to move the projection lens, this construction has the problems that adjustments relating to the force of the magnetic force or leaf spring are difficult and the secured position may in some cases be shifted by, for example, an undesirably applied external force.
The projection lens moving mechanism of the fifth example of the prior art uses a link mechanism to shift the position of projection on the screen by means of a motor. This example therefore has the problems that the structure of the moving mechanism is bulky, heavy, and moreover, expensive.
The projection lens moving mechanism of the sixth example of the prior art has the problem of complex structure. The reason for this is that it has a construction in which a lead screw rod is rotatably attached to the housing and engages with threaded hole provided in the projection lens and in which the lead screw rod is rotated by operating a manipulation means provided on the side surface of the housing to cause vertical movement of the projection lens.
It is an object of the present invention to provide a projection lens shifting mechanism for a projector that enables two-dimensional movement of a projection lens by a simple structure and with high accuracy, that enables easy and manual operation of this two-dimensional movement by way of a simple user interface, and that thus solves the above-described problems of the prior art.
To achieve the above-described objects, the projection lens shifting mechanism of the present invention is provided in a projector apparatus for projecting a light beam from a light source onto a screen by way of a projection lens to make an enlarged projection of an image rendered on a display device; the projection lens shifting mechanism comprises:
a base plate secured to the housing of the projection lens shifting mechanism, provided with a guide surface that is parallel to the display surface of the display device;
a moveable plate capable of rigidly holding the projection lens, and, when in a moveable state, moving in a prescribed direction parallel to the display surface of the display device while being guided by the guide surface of the base plate;
a holding plate linked to the moveable plate by way of elastic members; constituting, together with the moveable plate, an elastic clamping structure that holds the base plate from both sides with the base plate interposed between the holding plate and the moveable plate and that clamps the base plate by means of the elastic force of the elastic members; and, when an external force works against the elastic force to release the clamping, being rendered moveable to move integrally with the moveable plate in a direction parallel to the guide surface of the base plate;
an engagement structure that is interposed between the holding plate and the base plate, the engagement structure, when the clamping structure is clamping the base plate, engaging the holding plate with the base plate to place the holding plate in a locked state, i.e., a state in which the holding plate cannot move with respect to the base plate in a direction parallel to the guide surface of the base plate; and
an engagement-release structure for releasing the engagement brought about by the engagement structure and switching the holding plate from the locked state to a moveable state.
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The projection lens shifting mechanism of the present invention thus adopts a construction in which elastic members are used to constantly press the moveable plate against the base plate. This construction is able to prevent tilting of the projection lens both when in the locked state and when in the moveable state and is therefore able to, for example, prevent deterioration of resolution.
The clamping structure is preferably provided with elastic members and securing screws that are screwed from the side of said holding plate into threaded holes formed in the moveable plate through through-holes provided in said base plate; the elastic members being arranged between the heads of the securing screws and the holding plate to press the holding plate normally toward the base plate.
The elastic member may be a coil spring.
The engagement structure comprises friction members provided on the holding plate and protrusions provided at positions on the surface of said base plate that confront said friction members.
The friction members may be rubber members bonded to the holding plate.
The engagement-release structure preferably comprises a right-angle lever structure that has an axis of rotation included in a plane perpendicular to the optical axis of the projection lens to generate output torque that makes a right angle with respect to input torque.
The right-angle lever structure preferably comprises:
a first lever having an axis of rotation included in a plane perpendicular to the optical axis of said projection lens and two arms are substantially in the same plane; and
a second lever having an axis of rotation included in a plane perpendicular to the optical axis of the projection lens and two arms thereof form a right angle;
the first and second levers being arranged such that:
a second arm of the second lever is arranged interposed between the holding plate and the base plate;
torque for releasing the engagement is applied to a first arm of the first lever; and the torque is transmitted to a first arm of the second lever through a second arm of the first lever.
The engagement-release structure preferably comprises two right-angle lever structures that are opposite each other across said projection lens;
the first arm of the first lever of each of the right-angle lever structures curves in a shoehorn shape to conform with the contours of the projection lens; and
the first arm of the second lever engages with the holding plate, and receives the torque transmitted from the first arm of the first lever while engaging with said holding plate.
The projection lens shifting mechanism includes a rotation prevention device that guides the moveable plate along the guide surface of the base plate without rotation, the rotation prevention device having a translation structure that allows translation movement only in a vertical or in a horizontal direction with respect to the base plate, and the rotation prevention device further having a guide means that guides the moveable plate to translate in a horizontal or a vertical direction with respect to the base plate.
The adoption of this configuration enables the constitution of a simple user interface for moving and holding the projection lens by means of the minimum necessary construction wherein the moveable plate becomes movable by grasping the lever members, provided opposite across the projection lens, with the hands so as to clasp the projection lens, following which the moveable plate is held at a desired position by releasing the grasp on the lever members. In addition, since the focus ring and zoom ring are clasped and held by the lever structure when the projection lens is being moved, the focus ring and zoom ring do not move and do not require readjustment after the projection lens has been moved.
Explanation next regards the operation of the projection lens shifting mechanism of the present invention.
Friction members are bonded to the holding plate, and a powerful friction force is produced when the holding plate is pressed against the base plate, whereby the holding plate is held tightly against the base plate. The moveable plate is attached to the holding plate such that it moves integrally with the holding plate in the moveable state, and as a result, in the state in which the holding plate is pressed against the base plate and moreover the friction members on the holding plate are pressed against the base plate, the moveable plate is also held securely against the base plate.
By separating the holding plate from the base plate by means of the engagement-release structure, the friction members on the holding plate are separated from the base plate and the holding plate can be easily shifted with respect to the base plate. The moveable plate thus can easily move parallel to the guide surface of the base plate.
A construction in which the moveable plate is pressed against the guide surface of the base plate both when being held immobile and when in a moveable state can prevent the inclination of the projection lens at all times and thereby prevent problems such as deterioration of resolution. In addition, since the focus ring and zoom ring are clasped between and held by the lever members during movement of the projection lens, rotation of the focus ring and zoom ring can be prevented and no changes occur in the state of focus and zoom before and after movement of the projection lens. The above and other objects, features, and advantages of the present invention will become apparent from the following description referring to the accompanying drawings, which illustrate examples of preferred embodiments of the present invention.